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XIANGYU WANG,Wonhee Cho,Hyoung Won Baac,Dongsun Seo,Il Hwan Cho 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.2
In this paper, we propose a novel double gate vertical channel tunneling field effect transistor (DVTFET) with a dielectric sidewall and optimization characteristics. The dielectric sidewall is applied to the gate region to reduced ambipolar voltage (Vamb) and double gate structure is applied to improve on-current (ION) and subthreshold swing (SS). We discussed the fin width (WS), body doping concentration, sidewall width (Wside), drain and gate underlap distance (Xd), source doping distance (XS) and pocket doping length (XP) of DVTFET. Each of device performance is investigated with various device parameter variations. To maximize device performance, we apply the optimum values obtained in the above discussion of a optimization simulation. The optimum results are steep SS of 32.6 mV/dec, high ION of 1.2× 10<SUP>-3</SUP> A/ μ m and low Vamb of -2.0 V.
Chen, Yu-Chih,Baac, Hyoung Won,Lee, Kyu-Tae,Fouladdel, Shamileh,Teichert, Kendall,Ok, Jong G.,Cheng, Yu-Heng,Ingram, Patrick N.,Hart, A. John,Azizi, Ebrahim,Guo, L. Jay,Wicha, Max S.,Yoon, Euisik American Chemical Society 2017 ACS NANO Vol.11 No.5
<P>Considerable evidence suggests that self-renewal and differentiation of cancer stem-like cells, a key cell population in tumorgenesis, can determine the outcome of disease. Though the development of microfluidics has enhanced the study of cellular lineage, it remains challenging to retrieve sister cells separately inside enclosed microfluidics for further analyses. In this work, we developed a photomechanical method to selectively detach and reliably retrieve target cells from enclosed microfluidic chambers. Cells cultured on carbon nanotube polydimethylsiloxane composite surfaces can be detached using shear force induced through irradiation of a nanosecond-pulsed laser. This retrieval process has been verified to preserve cell viability, membrane proteins, and mRNA expression levels. Using the presented method, we have successfully performed 96-plex single-cell transcriptome analysis on sister cells in order to identify the genes altered during self-renewal and differentiation, demonstrating phenomenal resolution in the study of cellular lineage.</P>
WANG, XIANGYU,Cho, Wonhee,Baac, Hyoung Won,Seo, Dongsun,Cho, Il Hwan The Institute of Electronics and Information Engin 2017 Journal of semiconductor technology and science Vol.17 No.2
In this paper, we propose a novel double gate vertical channel tunneling field effect transistor (DVTFET) with a dielectric sidewall and optimization characteristics. The dielectric sidewall is applied to the gate region to reduced ambipolar voltage ($V_{amb}$) and double gate structure is applied to improve on-current ($I_{ON}$) and subthreshold swing (SS). We discussed the fin width ($W_S$), body doping concentration, sidewall width ($W_{side}$), drain and gate underlap distance ($X_d$), source doping distance ($X_S$) and pocket doping length ($X_P$) of DVTFET. Each of device performance is investigated with various device parameter variations. To maximize device performance, we apply the optimum values obtained in the above discussion of a optimization simulation. The optimum results are steep SS of 32.6 mV/dec, high $I_{ON}$ of $1.2{\times}10^{-3}A/{\mu}m$ and low $V_{amb}$ of -2.0 V.
Lee, Kyu-Tae,Baac, Hyoung Won,Park, Dong Hyuk,Ok, Jong G.,Park, Hui Joon IEEE 2018 IEEE photonics journal Vol.10 No.6
<P>We investigate the effect of a dielectric overlay in a planar microcavity on optical performances of colorful, see-through ultrathin amorphous silicon/organic hybrid solar cells, where a conventional Fabry–Pérot cavity is integrated with a cathode. The proposed colored solar cell devices show an enhanced transmission efficiency by optimizing both a thickness and a refractive index of the dielectric overlay at a resonance wavelength, which is primarily attributed to a better admittance matching. In addition, a purity of semitransparent red, green, and blue colors is improved by increasing a thickness of metallic layers in the microcavity with little sacrificing the transmission efficiency; thus, achieving a wide color gamut coverage as compared to conventional liquid crystal displays. Furthermore, mitigating reflection losses at complementary wavelength ranges and creating sharp resonances lead to an improved photocurrent generation from the semitransparent hybrid solar cells. The study described in this work provides insights and possibilities to enhance the characteristic performances of diverse applications, such as energy-efficient display technologies and decorative solar cells.</P>
Akter, Afroja,Yoo, Geonwook,Kim, Sangin,Baac, Hyoung Won,Heo, Junseok American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.5
<P>The electronic intraband absorption in InGaN nanodisks embedded in GaN nanowires with several kinds of cladding materials and without cladding was theoretically investigated. The cladding layer was 5 nm thick, and AlN, GaN, and Al0.4Ga0.6N were considered. The strain distribution, internal electric field, and intraband absorption in the nanodisks were calculated using the elastic energy minimization method and the single-band Schrodinger equation implemented in Nextnano3. For a plain nanowire without cladding, an inhomogeneous strain in the disk caused a piezoelectric field and deformation potential, yielding band-bending and a higher electron probability density in the periphery of the disk. An InGaN nanodisk embedded in a cladding GaN nanowire exhibited a higher intraband absorption. The case of the GaN cladding was optimal owing to the homogeneous surroundings of the disk.</P>
Hybrid Metal-Halide Perovskite-MoS<sub>2</sub> Phototransistor
Park, Youngseo,Lee, Sanghyun,Park, Hui Joon,Baac, Hyoung Won,Yoo, Geonwook,Heo, Junseok American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>Two-dimensional (2D) molybdenum disulfide (MoS2) has attracted much attention as a promising next-generation optoelectronic device. In particular, multilayer MoS2 has superior optical properties compared to mono-or few-layer MoS2 because of its higher density of states and wider spectral response. However, as the number of layers increases, multilayer MoS2 becomes indirect, resulting in poor light absorption and low photoresponsivity. Here, we report the enhanced photocurrent response of a multilayer MoS2 thin-film transistor by stacking an organometal halide perovskite (CH3NH3PbI3) layer on top of the multilyaer MoS2. With the perovskite overlayer, the photocurrent increased by two orders of magnitude, and thus our proposed hybrid phototransistor exhibited significantly enhanced photoresponsivity of similar to 1.1 A/W as well as detectivity of similar to 9 x 10(10) Jones compared to the MoS2 phototransistor without the perovskite layer. We also observe that the electrical properties change because of the effect of the overlayer. Our result indicates that multilayer MoS2 with a CH3NH3PbI3 overlayer can be a promising structure for high-performance MoS2-based photodetector applications.</P>
흰쥐의 좌골 신경 자극을 통한 광전 자극의 가능성에 대한 연구
김의태,오승재,박형원,김성준,Kim Eui tae,Oh Seung jae,Baac Hyoung won,Kim Sung june 대한의용생체공학회 2004 의공학회지 Vol.25 No.6
본 연구는 외부 전원 없이 광다이오드만을 이용하여 생성한 광전 자극을 통해 신경계를 효과적으로 자극하는 방법에 대한 것이다. 광을 통한 전류원 생성 및 전달은 생체 내에 집적된 광소자를 삽입하고 외부에서 광을 통해 신호와 전력을 전달을 한다. 이 기술은 특히 '눈' 이라는 광학적인 연결통로를 이용할 수 있는 인공망막과 같은 시스템에 매우 효과적이다. 그러나 광전 소자를 내부 전원 없이 구동시키는 경우, 광전류가 생체 저항에 직접적인 영향을 받게 되므로 자극에 충분한 전류를 생성할 수 없다. 무 전원 광다이오드를 통해 생성되는 광전류를 신경 자극에 적용하기 위해서는 생체 저항의 크기에 관계없이 활동 전위 생성에 충분한 전류 공급을 할 수 있는 안정된 전류원이 필요하다. 이를 위해서 본 연구에서는 병렬 저항을 도입하였다. 병렬 저항 추가 시 생체 저항을 포함한 전체 저항 값이 낮아지므로, 광원의 세기에 따라 최대의 광전류에 근접한 값을 얻을 수 있게 된다. 그러나 병렬 저항 값의 크기를 낮출수록 자극에 쓰이지 않는 전류량이 늘어나므로, 자극 전류량의 극대 값을 찾기 위해서는 병렬 저항 값의 최적화가 필요하다. 실험을 통해 측정된 실제 자극 전류량이 최대가 되는 병렬 저항 값의 범위는 500Ω∼700Ω 이고, 이때 전류량은 580uA∼860uA 이며 전류 효율은 47.5∼59.7%이었다. 자극의 크기와 빈1도를 변화시키면서 쥐의 좌골 신경을 자극하여 눈으로 확인 가능한 떨림 현상을 확인하였으며, 다채널 기록기를 이용해 활동 전위를 측정하였다. 이를 통해, 인공 망막에서의 광 자극 가능성을 확인할 수 있었다. A neural prostheses can be designed to permit stimulation of specific sites in the nervous system to restore their functions, lost due to disease or trauma. This study focuses on the feasibility of optoelecronic stimulation into nervous system. Optoelectronic stimulation supplies, power and signal into the implanted optical detector inside the body by optics. It can be effective strategy especially on the retinal prosthesis, because it enables the non-invasive connection between the external source and internal detector through natural optical window 'eye'. Therefore, we designed an effective neural stimulating setup by optically based stimulation. Stimulating on the sciatic nerve of a rat with proper depth probe through optical stimulation needs higher ratio of current spreading through the neural surface, because of high impedance of neural interface. To increase the insertion current spreading into the neuron, we used a parallel low resistance compared to load resistance organic interface and calculated the optimized outer parallel resistance for maximum insertion current with the assumption of limited current by photodiode. Optimized outer parallel resistance was at a range of 500Ω-700Ω and a current was at a level between 580uA and 650uA. Stimulating current efficiency from initial photodiode induced current was between 47.5 and 59.7%. Various amplitude and frequency of the optical stimulation on the sciatic nerve showed the reliable visual tremble, and the action potential was also recorded near the stimulating area. These result demonstrate that optoelectronic stimulation with no bias can be applied to the retinal prosthesis and other neuroprosthetic area.